Edit: I finished syncing and tested quickly rieMiner with your wallet via GetBlockTemplate. Unfortunately, I am getting "CheckProofOfWork() : not valid pow" messages in Testnet when finding blocks, but the miner seems to be able to extract correctly the mining information (else, it would not mine anything, yet it is actually working and finding/submitting things).

The GetBlockTemplate command in 0.16 seems to give the same results for the needed fields (previousblockhash, coinbasevalue, bits,...), so I think that the miner should still have been compatible without any changes. The version changed, but submissions are still rejected if I hard change it to 2. Can you see in your side what might have changed when the wallet receives proof of work?